Control system for stage encore curtain hoisting motors



Jan. 20, 1953 p FlscHER 2,626,375

CONTROL SYSTEM FOR STAGE ENCORE CURTAIN HOISTING MOTORS Filed Jan. 15, 1951 3 Sheets-Sheet l l fi I I? IQ EQ' I5 l b I9 I 7 I 7 I; mg] III .2: III I I -I I -I4 rfi wo 1 ELF-LOCK WORM GEARING POTENTIOMETER LIMIT -30 RHEOSTAT SWITCH Jan. 20, 1953 P. M. FISCHER 2,626,375

CONTROL SYSTEM FOR STAGE ENCORE CURTAIN HOISTING MOTORS I Filed Jan. 15, 1951 3 Sheets-Sheet 2 P. M. FISCHER Jan. 20, 1953 CONTROL SYSTEM FOR STAGE ENCORE CURTAIN HOISTING MOTORS Filed Jan. 15, 1951 3 Sheets-Sheet 3 Patented Jan. 20, 1953 CONTROL SYSTEM FOR STAGE ENCORE CURTAIN HOISTING MOTORS Paul M. Fischer, Milwaukee, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application January 15, 1951, Serial No. 266,096

(01. SIS-67) 10 Claims. 1

This invention relates to stage encore curtains, and more particularly to control systems for motors affording hoisting and lowering of such curtains.

The subject matter of the present invention is in certain respects similar to that disclosed in the Lassen and Seeger Patent No. 2,002,268, issued May 21, 1935, and is an improvement there- A primary object of the present invention is to provide a control system for each of the hoisting motors of a stage encore curtain which will afford most of the desirable features of a control system disclosed in the aforementioned patent and which will, in addition, afiord greater accuracy in controlling .the preselected range of operation and in regulating the preselected speed of such hoisting motors.

A more specific object of the invention is to provid a control system of the aforementioned character wherein the range of operation of each hoisting motor may be individually preselected from a plurality of preset but adjustable ranges by operation of a single control instrumentality.

Another object is to provide a control system of the aforementioned character wherein the base speed of operation of its associated motor is adjusted according to the range of operation preselected therefor so that such speed will be proportional to such range, thereby insuring that all motors will operate through the ranges preselected therefor in substantially the same interval of time, and

A still further object is to provide a control system of the aforementioned character wherein the speed of the motor is maintained substantially constant regardless of variations in the load to which it is subjected- Other objects and advantages of the invention will hereinafter beapparerit.

The accompanying drawings illustrate a preferred embodiment of the invention which will now be described, it being understood that the embodiment illustrated may be modified in respect of details without departing from the scope of the appended claims.

In the drawings:

Figure 1 is a front elevational view of the proscenium of a theatrical stage or the like, showing the stage curtain draped or drawn to a contour preselected therefor-a schematic arrangement of hoisting cables, hoisting drums, and drum driving motors being illustrated.

Fig. 2 is a more or :less schematic view in top plan showing the preferred arrangement of one hoisting drum, its associated driving motor and certain control apparatus driven by such motor.

Figs. 3 and 3 diagrammatically depict one driving motor and a control system for such motorFig. 3 shows the motor and the part of the control system more or less directly related to control of the motor, while Fig. 3 shov s that part of the control system relating principally to initiating and stopping the action of the part of the control system shown in Fig. 3 and 4 is a schedule of contactors and relays shown in Figs. 3 and 3 with their respective contacts shown m chanically coupled to their operating windings, and with such contacts arranged in alinement with the same contacts shown in Figs. 3 and 3 a Referring to Fig. 1, the numeral 10 designates in general the proscenium or border of a stage opening, behind which a curtain H (which may be termed the encore curtain) is hung or mounted, as by attaching the upper end or edge thereof to a fixed supporting bar on cable I2 the height of the curtain with respect to the proscenium on stage opening being such as to suit the particular requirements of an installation. The curtain H preferably is of a width considerably in excess of the proscenium whereby the desired fullness thereof to facilitate artistic draping is provided-the opposite ends H and N being preferably attached to cables l2 and [2 of fixed length which are in turn attached to bar 12. In Fig. l are shown five cables or ropes [3 to H, inclusive, attached to the rear edge of curtain H at spaced points alongthe lower edge thereof-the other ends of said ropes being respectively attached to sheaves or winding drums Ii, to Il inclusive, which drums are adapted to be rotated in opposite directions selectively by the motors i3 to HP to effect raising. and/or loweringof the corresponding portions of the curtain. Thus by properly-controlling the operation of the motors l3 to il inclusive, the curtain it may be lowered at will or drawn to substantially any desired contour. v

Fig. 2 shows a preferred arrangement for the hoisting drum 13% Drum I 3 and its associated driving motor [3 are mounted. on a supporting base (8, together with an associated potentiometer rheostat l9 and a limit switch 28. The driving motor is arranged to drive its associated drum through self-locking worm gearing 2| and a shaft 22. The adjusting element of the rheostat l9, and the driving element of the limit switch 20 are interconnected by a-shaft 23. Shaft 23 is driven by shaft 22 whenever the latter is rotating through an endless chain 2% running on sprocket wheels 22 and 23* fixed on shafts 22 and 23, respectively.

Use of the self-locking worm gearing 2! in the driving connection between driving motor [3' and hoisting drum le obviates need for an electrically controlled brake to maintain the position of such driving motor and hoisting drum upon stopping of the motor. The potentiometer rheostat [9 associated with each such motor and hoisting drum, as will be hereinafter more fully explained, is electrically connected in the control circuit of its associated motor and its adjusting element is moved through a range corresponding to the range of operation of its motor. The limit switch 26 associated with each of the potentiometer rheostats 19, is also electrically connected in a power for driving motor I3 and afiords circuit commutations at each of two opposite extreme limits to prevent operation of a driving motor beyond limits which might cause damage to the potentiometer rheostat 59. A preferred form for the limit switch 26 is shown and described in the Hodgson Patent No. 2,519,907; granted. August 22, 1950.

As will be understood, each of the other hoisting drums ic to ll will be similarly arranged.

with respect to their respective associated driving motors is to li and will, in like manner, have a potentiometer rheostat and limit switch, like rheostat is and limit switch 28, associated therewith.

Referring to Figs. 3 3 and 4, they show the motor 53*, which is preferably a direct current motor, and the control system for motor [3 It is to be understood that the control system now to be described for motor I3 would for the most part, be duplicated for each of the other motors lt to ii The part of the control system shown, and to be described, in connection with Figs. 3 and 4. contains certain control instrumentalities which are common to all the individual control systems for the other motors W to l7", and need not be duplicated for each such control system. These common control instrumentalities will be hereinafter more particularly pointed out.

The portion of the control system first to be described embraces the power supplies for the armature and field of motor l inclusive of the operating connections therefor. More particularly, power for energizing the armature a of motor I3 and the control system of the motor is supplied from a single phase alternating current source comprising supply lines L and L A transformer 26 has the end terminals of its primary winding 28 connected to lines L and L and has a multi terminal secondary winding 26 The left-hand end terminal of winding 26 is connected to the anode 27 of an electron discharge tube 2'? in series with a conductor Y28 and a primary winding 25 of the transformer 2-8. The right-hand end terminal of winding 26 of transformer 26 is connected to the anode 30 of an electron discharge tube 30, like tube 21, in series with a conductor 3! and a second primary winding 29 of transformer 29. The center-tap termi nal of winding 26 of transformer 26 is connected by conductors 32 and 33 to the upper terminal of armature a of motor I3 Winding 26 has a terminal intermediate its left-hand end terminal and center-tap terminal connected to a conductor 3d, and said winding has another terminal intermediate its center-tap and right-hand end terminal which is connected to a conductor 35.

Tubes 2'! and 3d are also provided with cathodes lit and th and control grids 21 and 353, respectively. The cathodes 2'! and 30 of said tubes are connected together, and are connectible to the lower terminal of armature a of the motor, either through contacts 26 of limit switch 20 and normally open contacts 1M of an electromagnetic contactor IM, or through contacts 2% of limit switch 2t and normally open contacts 2M of an electromagnetic 'contactor 2M. Cathodes Z'i and w are also connected through a parallel combination of a resistor 36 and capacitor Bl, and a resistor 38 to a conductor 39 to which the oathodes of the corresponding tubes of the control systems would preferably be connected in like manner. A filter capacitor ill is connected between control grid- 27 and cathode 27 of tube 27, and a similar capacitor 4! is connected between control grid 38 and cathode 53 of tube 38.

Field winding f of motor I3 is supplied with D. C. exciting current from the high potential bus 42 and low potential bus 43 of a ,D. C. source which may be of any preferred type furnishing supply of D. C. current at substantially constant voltage. Winding f is connectable to buses 32 and A3 for current flow in one directionupon closure of normally open contacts F and F of an electromagnetic contactor F, and is connectable to said buses for current flow in the reverse direction upon closure of normally open contacts R and R .of an electromagnetic contactor R. In the present control system, the direction of current flow through field winding 1 determines the direction of operation of motor is The speed of operation of motor I3 in either direction, is regulated by controlling the conducting periods .of the tubes 21 and so during their respective conducting half-cycles. That part of the control system pertaining to control and regulation of the conducting periods of tubes 21 and'38 will now be described. More particularly, a transformer '44 has the end terminals of its primary winding 44 connected to conductors 34 and 35 through conductors i5 and it, respectively, and said transformer is provided with a secondary winding 44 having a center-tap terminal. The end terminals of winding de are connected together in series with a capacitor ii and a resistor 43. The center-tap terminal of winding 44 is connected to control grid 27 of tube 21 in series with a resistor 39. The point common to capacitor 47 and resistor 48 is connected to control grid 30 of tube 3c in series with a resistor 50. Control grids 21 and 35 are connected together through the aforementioned resistors 49 and 50, and through resistors 5i and 52.

Transformer 44 is provided with another secondary winding 44 having a center-tap terminal. The and terminals of'winding 44 are connected to the anodes 53 and 53 of a full-wave rectifier tube 53 which has a cathode 53 The cathode 53 of tube 53 is connected to the anode 5t of the left-hand half of a duo-triode tube 5 3 in series with a capacitor 55,, and said cathode is also connected to the other anode 55 of the right-hand half of tube '5 in series with a resistor 55. Anodes 54 and Me of tube are connected together through a resistor 5i. Anode 56 has associated therewith the cathode 5 2 and control grid 55, and anode 54 has associated therewith thecathode 54 and control grid 5 Cathode 55 of tube .54 is connected to the point common to cathode .53 of tube Es-and capacitor 55 series with a resistor 58, an adjustable resistor 59, a resistor 66, the resistance element of a potentiometer rheostat BI, and a resistor 62. Control grid 54 is connected to cathode 63 of a full-wave rectifier tube 63 which has a pair of anodes 63 and 63. Anode 54 of tube 54 is connected by a conductor I54 to the point common to resistors 5| and 52. Cathode 54 is connected in series with a resistor 65 to a conductor 66.

It will be appreciated that two single triode tubes can be used in place of duo-triode tube 54 if desired.

The anodes 63 and 63 of tube 53 are connected to the end terminals of a secondary winding 29 of transformer 29 which has a centertap terminal. A resistor 61 is connected across anodes 63 and 53 of tube 63.

The center-tap terminal of winding 28 of transformer 29 is connected to conductor 66 in series with the resistance element of a potentiometer rheostat 88, which has its adjusting element connected to control grid 54 of the lefthand half of tube 54. A capacitor 59 and a resistor III are connected in parallel between control grid 54 of tube 54 and conductor 66. A capacitor II is connected between the center-tap terminal of winding 29 of transformer 29 and conductor 66. A half-Wave rectifier tube I3 has its cathode 13* connected to conductor 65 and its anode 13 connected to the point common to cathode 54 of tube 54 and resistor 58.

Normally closed contacts ICR of an electromagnetic contactor I CR connected in circuit between the adjusting element of rheostat GI and a conductor '14 in series with a parallel combination of a capacitor I5 and a resistor 15. Normally open contacts ICR. of contactor ICR are connected in circuit between capacitor 15 and resistor I6, and the point common to adjustable resistor 59 and resistor 69. Normally closed contacts 2M and IM of contactors 2M and IM are connected in series between conductor '74 and and the point common to cathode 53 of tube 53, capacitor 55 and resistor 56.

The part of the control system now to be described comprises a circuit for controlling the range of operation of the motor [3 in either direction. More particularly, a transformer TI has a primary winding 'II which has its end terminals connected to conductors 34 and 35, and has a secondary winding 'I'I with a center-tap terminal. The left-hand end terminal of winding 11* is connected to anode 18 of an electron discharge tube I8 in series with the electromagnetic operating winding DCR of a relay DCR, which has a series connected capacitor I9 and resistor 80 connected in shunt thereacross. The right-hand end terminal of winding li is connected to anode Gi of a tube 8!, like tube T8, in series with the electromagnetic operating Winding UCR of a relay UCR, which has a series connected capacitor 82 and resistor 83 connected in shunt thereacross.

Tube I8 is also provided with a cathode w a control grid 18 and a screen grid 78 Tube BI is likewise provided with a cathode BI a control grid SI and a screen grid 8P Cathodes 18 and B I of tubes I8 and 8I are connected together through a conductor 84, and to the center-tap terminal of winding 'I'I of transformer 'I'I through a conductor 85. Cathode I8 of tube 78 is also connected to a D. C. terminal of a full-wave rectifier bridge 86. A filter capacitor 8? isco-nnected between control grid 1% and cathode 58 of tube l8, and a similar capacitor 83 is connected between control grid ill and cathode 8I' of tube 8|. Control grid 18 of tube I8 is connected to the adjusting element of potentiometer rheostat I9 in series with a resistor 89, and control grid 8| of tube 8! is likewise connected to such adjusting element in series with a resistor 90. The screen grids I8 and Bl of tubes l8 and BI are connected together through a conductor SI.

Rectifier bridge 36 has its other D. C. terminal connected to conductor 84 in series with the resistance element of a potentiometer rheostat 92, and in series with a capacitor 93 which parallels the resistance element of rheostat 92. The adjusting element of rheostat 92 is connected to conductor 9!. The A. C. terminals of rectifier bridge 86 are connected to the end terminals of a secondary winding 94 of a transformer 9d, which has a primary winding 94 with its end terminals connected to conductors 45 and 46.

A transformer 95 has the end terminals of its primary winding 95 connected to supply lines L and L and is provided with a secondary winding 95*. One end terminal of winding 95' is connected to a conductor 96, which conductor is connected to a conductor 9! in series with an adjustable resistor 98. The other end terminal of winding 95 is connected to a conductor 99. The resistance element of potentiometer rheostat I9 is connected at one end to conductor $5 between adjustable resistor 98 and the first mentioned end terminal of winding 95*, and is connected at its other end to conductor 99. I

The rotary contact arm Oil of a rotary selector switch 590 is connectable to the point common to the adjusting element of rheostat I9, resistor 89 and resistor 90 through normally open contacts FOR of an electromagnetic relay FOR and a resistor It'll. A conductor I82 is connected to conductor at one end and at its other end to the point common to the right-hand contact of normally open contacts RCR of an electromagnetic relay RCR and resistor Iill. The lefthand contact of contacts RCR is connected to a conductor I93, and to stationary contact I of selector switch I05.

Selector switch I30 also has stationary contacts 2 to 8, inclusive. Contacts 2, 3 and l are connected to the adjusting elements of potentiometer rheostats I84, I05 and I66. respectively, which rheostats have their resistance elements connected in parallel across conductors 91 and H13. Although not shown, it may be assumed that a plurality of other potentiometer rheostats, like rheos-tats IE4, IE5 and 965, have their resistance elements connected in parallel across conductors 9'! and I03 and have their adjusting elements connected to contacts 5, 6, 'i and 8 of selector switch I E38, respectively. The rotary contact arm Hill of selector switch IElii is mechanically connected to the adjusting element of potentiometer rheostat -6I to afford adjustment of such element in accordance with the switch position selected.

An adjustable resistor ID! is connected at one end to the point common to the lower end of the resistance element of rheostat I9 and conductor 99 and is connected at its other end to the point common to the right-hand contact of normally closed contacts ICR of relay I CR, the right-hand contact of normally open contacts RCR of relay RCR. and the left-hand contact of normally open contacts FCR of relay FCR.

An adjustable resistor I08 is connected at one 'end to conductor 91 and at its other end to the right-hand contact of contactsFCR in series with normally open contacts I CR of relay ICR.

Referring to Figs. 3 tandilthey'show that part of "the 'control'system .havingzto do with .initiating and stopping the action of those'parts of the control system hereinbefore "described. More particularly, conductor 34 is connected through normally closed contacts of push-button switch M5 to a conductor III A push-button switch H2 has its normally open contacts H2 connected through its left-hand contact to conductor I II, and through its right-hand contact through normally closed contacts ILR of an electromagnetic latching relay ILR, the operating winding F cf contactor F, normally closed contacts R of contactorR, and conductor H3 to conductor 35. The right-hand contact of contacts H2 is also connected in circuit with the left-hand contact of contacts I I2 of said switch and the left-hand contact of normally open contacts ICR of relay lCR. Contacts ILR are also connected through the right-hand contact thereof to the left-hand contact of contacts IM of contactor IM.

Contactor F has normally open contacts F which are connected in circuit with conductor i l l, the left-hand contacts of normally-open contacts 1M and UCR- of contactor IM and relay UCR respectively, and to the left-hand end of the oprating winding FCR of relay FCR. The righthand contact of contacts UCR is connected through the operating winding lit 5 of contactor 5M to conductor 1 l3.

Contacts IIZ of switch II2 are connected through the right-hand contact thereof to the left-hand contact of normally closed contacts IIS of a push-button switch H5. The right hand contact of contacts .I'IG is connected through normally closed contacts ILR of relay 11R, and the operating winding ILR' of relay lLR to a conductor I H, which is connected at one end to the point common to the operating winding F of contactor F and the left-hand contact of contacts R of contactor R.

The right-hand contact of contact mm of relay ICE is connected to conductor H7 in series with normally closed contacts 2LR of an electromagnetic latching relay 2LR and the operating winding ZLR of said relay. Normally open contacts H are connected through the lefthand contact thereof to conductor III, and through the right-hand contact thereof to a conductor II8, which is connected to the point common to the right-hand contact of contacts I CR and the left-hand contact of contacts 2LR Contactors F and R have normally open contacts F and R respectively, which are connected through their left-hand contacts respectively to conductor III, and though their righthand contacts, respectively to the left-hand contacts of contacts ZL-R and 'ICR of relays 21 R and 1GB, respectively. Contacts ZLR and 1GB, are connected through their respective righthand contacts to the operating winding I CR of relay ICR, having connection with conductor H3.

Contactor 'R also has additional normally open contacts R which are connected through the left-hand contact thereof to conductor I i l. The right-hand contact of contacts R is connected in circuit with normally open contacts 2M of contactor 2M, the operating windingR of cont'actor R, normally closed contacts F of contactor F to conductor H3, Thelast mentioned contact of contacts R is also connected in circuit with normally open contacts DCIR and the operating winding 2M3 of contactor 2M to con- 8 ductor. H3, :and, with the "operating winding .RCR of relay .RCR to'conductor I I3.

A push-button switch 121 has its normally open contactsfll l' connected through the lefthand contact thereof to conductor III. The right-hand contact of contacts Illl is connected to thepointcommon to the right-hand contact of contacts 2M and the operating winding R-of relay R. Such right-hand contact -of contacts 'I2'l is also connected in circuit with the normally closed contacts IZ'I of switch I'ZI. The right-hand contact of contacts I2 I is connected in circuit in series with :normally open contacts ILR of relay 11R, and the lat'chtripping winding11R o'f'relay I'LR. Such righthand contact of contacts I2I is also connected in circuit in series with contacts ZLR of relay ZLR and the latch-tripping winding ZLRF of 'relay ZLR.

A's aforementioned, certain of the initiating and stopping control instrumentalities would not be duplicated in the control systems for each of the other motors 14 to II". "More particularly, these control instrumentalitie's comprise the contactors .F and R and their respective contacts, the latching relays ILR and ZLR and their respective operating and latch-tripping windings and contacts, the relays 'FCR, RCR, and ICE and their respective contacts, and the push-button switches H0, I12, I I6 and '-l2-I and their respective contacts. V

Conductors 122' and I23, having connection with the end terminals of winding 25 of transformer '25, maybe assumed to be connected in circuit with the primary windings of transformers, corresponding to windings 253 andzs' of transformer 29 in the control systems of each of the other motors. Likewise conductor I24 and I25, having connection with the aforementioned intermediate terminals of winding 26 of transformer 26, may be assumed to furnish power to the primary windings of transformers, corresponding to primary winding W of transformer H, in the control systems of each of the other motors. Each of the conductors 33, 39, 9t, 97, 99, and I523 may be assumed to respectively connect with a corresponding conductor in the control systems of each other of the other motors.

The operation of the control system motor I3 will now be described.

Let it be assumed that all points of the loot tom edge of curtain II are at stage level. Also let it be assumed that contacts 26 of limit switch 23 are closed and that the rotary contact arm we of selector switch Hill is in the position, wherein the adjusting arm of rheostat 61 is given a corresponding setting as depicted in Fig. 3 So long as switch 119 is closed, conductor ill will be connected to and "at the same potential as conductor 34.

Assume that it is desired to raise the curtain l I to the contour shown in Fig. l, where the point of the bottom edge of curtain ii to which cable I3 is attached is drawn to the level depicted. Raising of the curtain is initiated by momentary "operation of switch IIZ. Such operation of switch H2 effects closure of its contacts H2. Closure of contacts I l2 completes a circuit from conductor HI, t rough contacts I 1.2 contacts E3 of latching relay fL-R, the operating winding F of contactor F, the contacts R of contactor R, and conductors H3 to conductor '35, thereby energizing the operating winding F oi contactor F. Contacts F F F and F of contactor F thereupon close and contacts F of said contactor open. Closure of contacts F and F, as aiorein'dicated, effects connection of field winding 3 of motor I3 to buses 42 and 43 for flow of D. C. exciting current therethrough in one direction, which may be assumed to be that direction which will effect rotation of the armature a in the forward direction, affording reeling-up of cable It on drum I35 Closure of contacts F completes a circuit from conductor I I I, through the operating winding FCR of relay FCR, and conductor H3 to conductor 35, to thereby energize the operating winding FCR. of relay FCR. Closure of contacts F has no effect upon the control system under the conditions being described, The opening of contacts F prevents the energization of the operating winding R of contactor R, as by accidental operation of switch I2 I.

Energization of the operating winding FCl-i. of relay FCR effects closure of its contacts FCR and FCRP. Closure of contacts FCR completes a circuit from the adjusting element of rheostat W4, through stationary contact 2 and rotary contact arm Hid of selector switch I00, and resistor it! to the point common between the adjusting element of rheostat I9, resistor 89 and resistor 90. With the adjusting element of rheostat IS in the initial position depicted in Fig. 3 the A. C. potential at the left-hand end of resistor IOI will be greater than the A. C. potential at the righthand end thereof affording a potential drop thereacross to which the control grids 78 and 85 of tubes I8 and BI are subjected. Such potential is out-of-phase with the A. C. potential of the anode 18 of tube 18 and in-phase with the A. C. potential of the anode 8I of tube 0|. Consequently tube BI is rendered conducting while conduction of tube I8 is blocked. Initiation of conduction of tube 8| causes the operating winding UCR of relay UCR to be energized and remains energized so long as tube -8I is maintained conducting.

Energization of the operating winding UCR of relay UCR effects closure of its contacts UCR Closure of contacts UCR. completes a circuit from conductor I I I, through the then closed contacts F contacts UCR the operating winding IM of contactor IM, and conductor II3 to conductor 35, to thereby energize the operating winding of contactor IM.

Energization of the operating winding IM of contactor IM effects closure of its contacts IM and lid and opening of its contacts III/I Closure of contacts IM completes a connection from the center-tap terminal of the secondary winding 20" of transformer 26, through conductors 32 and 33, armature a of motor I3", contacts Il /l and contacts 20 of limit switch 20, to the cathodes 27 and 30 of tubes 21 and 30, thereby completing the operating power connections for motor I3 to enable its running in the forward direction. Closure of contacts IM completes a circuit from conductor lII, through the then closed contacts F contacts IMF, the oper- 1 ating winding F of relay F, contacts R and conductor I 3 to conductor 35, to provide a maintaining circuit for the operating winding F of relay F upon release of switch H2. The opening of contacts IM interrupts the charging connections for'capacitor I5.

' When switch H2 is released the contacts Iii reopen and the contacts II2 reclose. Reclosure of contacts H2 completes a circuit from conductor HI, through the then closed contacts F and IM contacts ILR contacts IIZ contacts IIB, contacts ILR the operating winding ILR of relay ILR, contact R and conductor II3 to conductor 35, to thereby energize operating winding ILRC of relay ILR. Energization of operating winding ILR effects opening of contacts ILR and ILR and closing of contacts ILR Opening of contacts ILR. and ILR. interrupt the circuit through operating winding ILR' thereby deenergizing the same, but due to the mechanical latch ILR falling in place, the contacts of relay ILB remain in the aforementioned operating portions attained by the momentary energization of operating winding ILRF.

Motor I3 will have an operating speed as dictated by the setting of the adjusting element of rheostat GI. Such setting of the adjusting element of rheostat BI is dependent upon the operating position selected for selector switch I00, due to the aforementioned mechanical connection between the adjusting element of rheostat SI and the rotary contact arm I00 of switch I00.

The range of operation of motor I3 in the forward direction is dictated by which of the rheostats I04, I05, I06, etc., has its adjusting element connected in circuit with the control grids 18 and 8I of tubes I8 and 8|. It has been assumed in the present instance that the adjusting element of rheostat I04 is in circuit with the last mentioned control grids.

With rheostat I04 in circuit with control grids l8 and 81, the setting of the adjusting element of rheostat SI will be such, that the operating speed of motor I3 will be proportional to the range of operation in the forward direction preselected therefor.

As will be understood, the arrangement of the range determining rheostats and speed determining rheostats will be the same in the control systems for each of the other motors M to I'I so that the points on the bottom edge of curtain to which the cables I3 to II are attached will arrive at their respective final levels, to provide a desired contour, at substantially the same instant. In other words, all of the motors I3 to I'I will operate through their respective preselected ranges in substantially the same interval of time; their respective base speeds being proportional to the particular range through which they opcrate.

It will be appreciated that the secondary winding 44 of transformer 44, capacitor 41 and resistor 43 comprises a phase-shift network affording an A. C. potential, having a fixed phase angle with respect to the A. C. potential on the anodes of tubes 21 and 30, to which the control grids 21 and 30 of tubes 21 and 30 are subjected. This A. 0. potential is superimposed on a D. C. potential which varies in magnitude as will now be explained.

The secondary winding 44 and full-wave rectifier tube 53 afford a source of rectified voltage. Control grids 21 and 30 of tubes 21 and 30 are connected to the cathode of tube 53 through conductor 64 and resistors 51 and 50 and would be subjected to a constant unidirectional potential except for the effect of IR compensation and current limiting circuits as will be hereinafter explained.

Capacitor I5 and resistor I6 are connected through conductors I4 and 19, and resistor 30 to cathodes 2! and 30 of tubes 21 and 30, and through contacts ICE. to the adjusting element of rheostat BI. Capacitor I5 is also connected to the cathodes of tube 53 whenever contacts IM and 2M of contactors IM and zlvL respectively, are closed. Thus, prior to operation of switch I I 2, capacitor 15 will be charged to the potential of the cathode 53 of tube 53, and consequently, the potential of the grids 27 and 36 of tubes 2? and 30 will be substantially that of their asso' ciated cathodes 21 and 38 When contact IM opens, as a result of operation of switch I i2, capacitor i is disconnected from cathode 53 of tube 53 and then discharges through the resistor 76. Consequently the potential of grids 2i and tid rise relative to the cathodes 27 and 39, thereby rendering the tubes 21 and 30 increasingly conducting, until capacitor 75 discharges to the potential-of the adjusting element of rheostat at, which determines the normal level of conductivity of tubes 27' and 30. It will thus be apparent that armature a is not subjected to full potential instantaneously, but rather according to the time constant of the capacitor and resistor it, and until the current limit circuit, hereinafter explained, can take over acceleration to the preselected operating speed.

It will be appreciated that the load on motor it? will not be constant during its range of operation in the forward direction. This is due to the fact that as curtain H is drawn upwardly it folds or drapes and the loading will not be equal on all the cables I3 to H and will change on these various cables as the curtain is drawn up to a preselected contour. Thus IR or load compensation is provided in the present control system. If the load on the armature (2 increases, the current drawn by thearmature will increase causing increase in the current flowing in the windings 129 and 29 of transformer 29. Increased current flow in windings 29 and 29 results in increased potential induced 1n secondary winding 29 of transformer 29. Consequently, the potential of the adjusting element of rheostat 83 increases in the negative sense relative to the conductor'fit, thereby-increasing in a negativesense the potential of control grid 5% relative to cathode 5 3 in the right-hand half of duo-triode tube 5 3. conductivity of the right-hand half of tube 54, thereby causing'increase in the magnitude of the unidirectional potential to which control grids 21 andtii of tubes 21 and are subjected. As a result tubes 21 and 3!] are caused to fire earlier in their respective conducting half -cycles, thereby increasing the flow ofv current to armature a to maintain thespeed of motor 13* at preselected value. As will be understood, the reverse of the aforedescribed action occurs upon decrease in load on armature a.

The aforedescribed IR compensation is subject to current limiting action afforded by the left-hand half of tube 5%. This half of the tube is normally non-conducting. As the potential induced in winding 29 of transformer increases, the potential of control'grid 54c increases relative to cathode e i and upon sufiicient increase in such potential the left-hand half of tube 5e becomes suddenly conducting to thereafter, not only prevent further increase, but also to de creasethe unidirectional potential towhich control grids 27 and 39 of tubes fl'and 3e-aresubjected. Thus the conduction of the left-hand half of tube 54 definitely limits the maximum effective current thatfcan be supplied by tubes 2? and 3B, and hence the maximum current that can be drawn by the armature a of motor i3 'As the armature a rotates in the forward direction, the adjusting element of rheostat 19 may This results in decreased 12 be assumed to be driven in the clockwise direction (as shown in 3*) relative to its associated resistance element. As the adjusting element of rheostat l9 advances in the clockwise direction the potential drop across r sistor 19! decreases, and approaches a potential, the magnitude of which is determined by the adjustment of potentiometer rheostat 22, which prevents further conduction of tube 8%. Consequently, the operating winding UCR. of relay UCR is deenergized with resulting opening of the contacts UCR Opening of contacts UCR results in deenergization of the operating winding lid of ccntactor IM, with following opening of its contacts ill/I and IM and closing of its contacts 1M As will be readily understood, all relays and contactors which were energized as an incident to operation of switch H2, will thereafter be deenergized, and the power connections to the field f and armature a of motor it will be interrupted. Motor 33* thereafter comes to rest immediately due to the locking action afforded by self-locking worm gearing 2! in the connection between said motor and hoisting drum i3 driven thereby.

It will be appreciated that if selector switch 80 were positioned to connect one of the other rheostats E I34, I05, etc/in circuit with the control grids 78 and 8! of tubes i8 and 35, the range of operation of motor W in the forward direction would be different and would depend upon the adjustment of the adjusting element of the particular rheostat of the group we. let, etc. connected in circuit.

If thecurtain H is at stage level and the rotary contact arm lat of switch N38 is in engagement with stationary contact i, then motor if) will not be energized as no potential drop would exist across resistor lei. Such positioning of selector switch H38, thus permits maintaining the points of curtain lito which cable i3 is attached at stage level when desired in certain contours.

The control systems for the other motors i to 11 would have a similar arrangement of range controlling rheostats and selector switch. Thus a desired contour may be readily preselected by appropriate positioningof the selector switches of each of thecontrol systems for the motors 13 to If. Although not shown, all of such selector switches would preferably be grouped together on a common control panel so as to facilitatethe setting of a desired contour by an opera-tor.

Assume now that the curtain H is at the contour shown in Fig. 1, and it is desired to return it to stage level. Momentary operation of switch I2! aifords initiation of functioning of the control system of motor l3 for operation in the reverse direction to effect lowering of cable 13 as will now be described. Such operation of switch 12! effects closure of its contacts I2 I and opening of its contacts l2l Closure of contacts l2! completes a circuit from conductor Hi, through contacts l2l the operating winding R of contactor R contacts F and conductor H3 to conductor 35, thereby energizing the operating winding R of contactor R.

Energization of the operating winding R. of contactor R results in closure of its contacts R R R and R Closure of contacts R and R. effect the connection of field f of motor i3 across buses 42 and 43 so that the iiow of energizing current through such field will be that required for rotation of armature a in the reverse direction. Closure of contacts R has no effect in the present operation of the control system. Closure of contacts R establishes a circuit from conductor III, through the operating winding RCR, of relay RCR, and conductor I I3 to conductor 35, thereby effecting energization of the operating winding RCR, of relay RCR. Opening of contacts F prevents establishment of a circuit through the operating winding F oi contactor F, as by accidental operation of switch I I2. Energization of the operating winding RCR of relay RCR results in closure of its contacts RCR and R03 Closure of contacts RCR establishes a circuit from conductor I03, through stationary contact I of switch I00, contacts RCR, and resistor Iill to the point common between the adjusting element of rheostat I9, resistor 89 and resistor 98.

It will be understood that the adjusting element of rheostat It would initially be at some position between that depicted in Fig. 3 and the lower end of its associated resistance element. The left-hand end of resistor IOI will be at the A. C. potential of conductor I03 and the adjusting element of rheostat I9 will be at some higher A. C. potential. The control grids 18 and 8| of tubes l8 and BI will thus initially be subjected to a net A. C. potential which is in phase with the anode potential of tube I8 and out-of-phase with the anode potential of tube BI. Such A. C. potential will be sufiiciently high to render tube I8 conducting, and of course conduction of tube 8| will be blocked.

The operating winding DCl-t of relay DCR becomes energized upon tube I8 being rendered conducting and the contacts DCR of relay DCR close. Closure of contacts DCR. establishes a circuit from conductor I I I, through the then closed contacts R contacts DCR the operating winding 2M of contactor 2M, and conductor II3 to conductor 35, thereby efiecting energization of the operating Winding 2M of contactor 2M.

Energization of the operating winding 2M of contactor 2M results in the closure of its contacts 2M and 2M and in opening of its contacts 2M Closure of contacts 2M establishes a circuit from the center-tap terminal of secondary winding 26* of transformer 26, through conductors 32 and 33, armature a, contacts 2M and contacts 20* of limit switch 20 to the cathodes 21 and 38 of tubes 21 and 30, thus completing the power connections for motor I3 Closure of contacts: 2M provides a maintaining circuit for the energizing winding R of contactor R so that the same will be maintained energized following reopening of contacts I2 I upon release of switch I2I.

When switch I2I is subsequently released contacts I2 i reopen and contacts I2 I reclose. Reclosure of contacts I2I establishes a connection from conductor I I I, through the then closed contacts R contacts 2M contacts I2I th then closed contacts ILR the latch-tripping winding I LR of relay ILR, contacts F and conductor I I3 to conductor 35 to eiTect energization of winding ILT Energization of winding ILR afiords release of the mechanical latch ILR, and relay ILR is thus returned to its normal operatingcondition preparatory to its reoperation as a result of operation of switch H2.

Motor l3 thereafter operates in the reverse direction. The behavior of the part of the control system regulating the conduction of tubes 21 and 36 will be the same as hereinbefore described.

Due to the closure of contacts RCR and because contacts FClt are then open, the potential of the adjusting element of rheostat I9 will be compared with the A. 0. potential at the lefthand end of resistor Illl. Now as the adjusting element of rheostat I9 is driven in the anti-clockwise direction as a result of operation of motor I3 in the reverse direction, its potential will decrease in magnitude. When the potential drop across the resistor IDI becomes substantially zero, the A. C. potential on control grid 18 decreases to a value at which tube I8 is cut off. As a result, the operating windin DCR of relay DCR is deenergized thereby efiecting opening of contacts DCR Opening of contacts DCR results in deenergization of the operating winding 2M of relay 2M and the contacts 2M thereupon efiecting deenergization of the operating winding R. of contactor R. The contacts R R R and R thereupon open resulting in interruption of the power connector to the field ,f; the power connections to armature a having previously interrupted by opening of contacts 2M Motor I3 is thus stopped and the point of the bottom edge of ourtain II to which cable I3 is attached will then be at stage level.

The control systems for the other hoisting motors I4 to I'I will operate in a similar manner and the points to which their associated cables are attached will arrive at stage level substantially simultaneously with the point to which cable I3 is attached.

When it is desired to raise curtain I I clear of the proscenium of the stage, with all points of the bottom edge of the curtain being raised above the upper border of the proscenium at the same rate of speed, such can be accomplished in the resent control system by momentary operation of switch I I6, regardless of the setting of selector switch I69 and of the corresponding selector switches in the control systems of the other motors.

Let it be assumed that all points of the bottom edge of curtain II are at stage level, and that switch I I6 is momentarily operated. Such operation of switch IIB results in opening of its contacts Ill; and in closing of its contacts IIG Closure of contacts III; completes a circuit from conductor II I, through contacts IIB the operating winding ICR. of relay ICR, and conductor 3 to conductor 35, thereby energizing the operating winding ICR of relay ICR. Energization of the operating windin ICR. of relay ICR effects closure of its contacts ICR ICR ICE. and ICR and opening of its contacts ICE. and ICR.

Closure of contacts ICR. completes a circuit from conductor I I I, through the then closed contacts I16", contacts ICR contacts lLR the operating winding F of contactor F, contacts R and conductor II3 to conductor 35, to thereby energize the operating winding F of contactor F. Contacts F F F and F thereupon close, and contacts F open. Thus the power connections for the field f are completed for operation of motor I3 in the forward direction. Closure of contacts F of course effects energization of the operating winding FCR of relayFCR and the contactsFCR. and FCR close. Closure of contacts F establishes a maintaining circuit for the operating winding F of contactor F from conductor III, through contacts F the then closed contacts ICE and ICR contacts ILR the operating winding 35 of contactor F, etc., to conductor 35, to maintain such operating winding energized following reopening of contacts I I6.

-The opening of contacts ICR disconnects the adjusting element of rheostat 6! from capacitor 15 and resistor 76, and the closure of contacts ICRL connectsc'apacitor l and resistor 16 to The closure of contacts F'CPJ- connects the ad just-mg element of rheostat l-fi l to the left-hand end of resistor Hill as before, but because the contacts CR open, the conductor Hi3 will be at the same potential as conductor 9?. Closure of contacts [CW and FUR? completes a circuit from conductor 91 through resistor I98 and contacts 1CR and FCR to the lower end of adjustable resistor I07.

Thus, even though selector switch I 99' mayhave. its rotary contact arm 108 engaged with stationary contact 2, the adjusting element of rheostat Ifit wiilbe essentially at the potential of conductor 9?. Due to the inclusion of the ad'- justable resistor 28 in circuit, the adjustin element of rheostat lfi will have to be driven farther in the cl-ockwisedirection before a point is reached where the potential drop across resistor Ill! becomes substantially zero. Preferably, the resistor I63 would also be included in circuit in the control systems for the motors l i to IT; the one resistor I88 serving for all the control systems to. insurethat all the mctorswill operate through identically the same range.

Tube 8'! upon closure of contacts FCR FCR and IE and opening of contacts ICR of course becomes conducting. to energize the operating winding UCI-t of relay UCR. Energization of the operating wiiuiingUCR of relay UCR, as hereinbefore explained, results in completion of the power connection to armature a of motor and said motor commences .to operate in the-forward direction. The partflof. the control system a-ffording supply and regulation of current to the armature aoperates as hereinbeforedescribed;

The closure of contacts He of switch H6 alsocompletes a circuit from conductorrlfl, through contacts ELF the operating: winding ZLR? of. latching, relay ELR and conductors H1, H 3 to conduct-or therebyenergizing operating winding' ELR As a result, contacts. 2LR and 21512 close, and contacts ZLR open. Opening'of contacts ZLPU interrupts the circuit through theop subsequent operation of'switch I21, an energizing circuit will be established for the latch-tripping winding 2L8 to afiord release of relay zLR for return to its normal operating position.

W'henswitch H6 is released its contacts HE reclose and its contacts H6 reopen. R'eclosing. of contacts lit completesa circuit from conductor ll'l, through contacts F through either contacts ICR or ZLR through conductor H8,

contacts ICR the then closed contacts H? of" switch IE2, contacts l'lt ',contacts lLR operating winding ILR of relay ILR, conductor Iii'l, contacts R and conductor H3 to conductor 35', thereby to energize operating winding ILR of relay ILR. Such energization of winding-ILR results in contacts SR and ILR being opened and maintained open until switch |2| is some quently operated.

Motor [3 will continue to operate in the forward direction and as the adjusting element of rheostat I9 is driven the clockwise direc tion, the A. C. potential between conductor 97 and the right-hand end of resistor It! will decrease in value until a point is reached where there is substantially zero potential drop across resistor Ill! and tube Bl will then be cut ofi to thereafter cause stopping of motor [3 in the manner hereinbefore described; When motor [3 has stopped it may be assumed that the point of the bottom edge of curtain II to which cable I3 is attached has been raised to some level above the upper border of theproscenium,- and that all the other motors [4 to li have efie'cte'd raising of all other points of the bottom edge of curtain II to the same level.

When curtain H has attained such a level and itis desired to return it to stage level, such is attained by operation of'switch [2| which functions to initiate operation motor [3 in the reverse direction in the manner hereinbefore described.

Operation of switch. HG, during operation of motorin either the forward or reverse directions afiords stopping of the same, it being apparent that openingofthe switch H0 affords deenergization' of all contacto'rs and relays that may then be energized.

I claim:

1. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors, of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means settable at will to preselect anyone of aplurality ofpreset but adjustable ranges of operation for its associated motor, and means for supplying the armature of said associated motor with rectified current including means responsive to the setting of. the first mentioned means to regulate the armature current in accordance with the range of. operation selected for said associated motor, and control means common to theco'nt'rol systoms of all of said motors for initiating operation of all of said motors in the same direction simultaneously;

2. In a contour system for stage encore curtains or the like, the. combination with a plurality of reversible direct current hoisting motors, of control systems individual to each of said motors'to be subjected to supply from an alternating current source comprising means settable atwill to preselect anyone of a plurality of preset: but adjustable ranges of operation for its associated motor, and means for supplying the armature of said associated motor with rectified current including means responsive to the setting of the first mentioned means to regulate the armature current in accordance with the range of operation selected for said associated motor, and further including means responsive to variations in load on said associated motor to rogu late the current supplied to its armature for constant speed operation, and control means common to-the control systems of all of the motors for initiating operation of all of the motors in the same direction simultaneously.

3. In-a contour system for stage-encore curtains or the like, the combination with a plurality of reversible direct currenthoisting motorsof control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means settable at will to preselect anyone of plurality of preset but adjustable ranges of operation for its associated motor, and means for supplying the armature of said associated motor with rectified current including means responsive to the setting of the first mentioned means to regulate the armature current in accordance with the range of operation selected for said associated motor, means responsive to variations in load on said associated motor to regulate the current supplied to its armature for constant speed operation, and further including means for limiting the maximum value of current supplied to the armature of said associated motor, and control means common to the control systems of all of the motors for initiating operation of all of the motors in the same direction simultaneously.

4. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors, of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means settable at will to preselect anyone of a plurality of preset but adjustable ranges of operation for its associated motor and means for supplying the armature of said associated motor with rectified current including means responsive to the setting of the first mentioned means to regulate the armature current in accordance with the range of operation selected for said associated motor, and control means common to the control systems of all of the motors comprising means for initiating operation of all of the motors in the same direction through the ranges individually preselected therefor, and further comprising means for initiating operation of all of the motors in the same direction through the same predetermined range regardless of the individual ranges preselected therefor by the first mentioned means.

5. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors, of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means for controlling the range of operation of its associated motor including a plurality of potentiometer rheostats and a selector switch settable at will to render anyone of said rheostats efiective to determine the range of operation of said associated motor in accordance with its setting, and means for supplying the armature of said associated motor with rectified current including means responsive to the setting of said selector switch to regulate the armature current in accordance with the range of operation selected for said associated n 1 o tor, and control means common to the control system of all of said motors for initiating operation of all of said motors in the same direction simultaneously.

6. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means for controlling the range of operation of its associated motor including a plurality of potentiometer rheostats and a selector switch settable at will to render anyone of said rheostats efiective to determine the range of operation of said associated motor in accordance with its setting, and means including controllable full-wave rectifying means for supplying the armature of said motor with rectified current and further including means responsive to the setting of said selector switch to regulate the output of said rectifying means in accordance with the range preselected for said associated motor, and control means common to the control systems of all of said motors for initiating operation of all of said motors in the same direction simultaneously.

7. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means for controlling the range of operation of its associated motor including a plurality of potentiometer rheostats and a selector switch settable at will to render anyone of said rheostats effective to determine the range of operation of said associated motor in accordance with its setting, and means including controllable full-wave rectifying means for supplying the armature of said associated motor with rectified current, means responsive to the setting of said selector switch to regulate the output of said rectifying means in accordance with the range preselected for said associated motor, and further including electronic means responsive to variations in load on said associated motor to regulate said rectifying means to afford constant speed operation of said associated motor, and control means common to the control systems of all of the motors for initiating operation of all of the motors in the same direction simultaneously.

8. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors, of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means for controlling the range of operation of its associated motor including 9, plurality of potentiometer rheostats and a selector switch settable at will to render anyone of said rheostats effective to determine the range of operation of said associated motor in accordance with its setting, and means including controllable full-wave rectifying means for supplying the armature of said associated motor with rectified current, means responsive to the setting of said selector switch to regulate the output of said rectifying means in accordance with the range preselected for said associated motor, electronic means responsive to variations in load on said associated motor to regulate said rectifying means to aiford constant speed o eration of said associated motor, and further including electronic means which acts to limit the maximum value of current supplied by said rectifying means, and control means common to the control systems of all of the motors for initiating operation of all of the motors in the same direction simultaneously.

9. In a contour system for stage encore curtains or the like, the combination with a plurality of reversible direct current hoisting motors, of control systems individual to each of said motors to be subjected to supply from an alternating current source comprising means for controlling the range of operation of its associated motor including a plurality of potentiometer rheostats 19 and a selector switch settable at will to render anyone of said rheostats efiective to determine the range of operation of said associated motor in accordance with its setting, and means including controllable full-wave rectifying means for supplying the armature of said associated motor with rectified current, means responsive to the setting of said selector switch to regulate the out- .put of said rectifying means in ccordance with the range preselected for said associated motor, electronic means responsive to variations in load on said associated motor to regulate said rectifying means to afiord constant speed operation of said associated motor, and further including electronic means which acts to limit the maximum value of current supplied by said rectifying means, andcontrol means common to the control systems of all of the motors comprising means for initiating operation of all of the motors in the same direction through the ranges individually preselected therefor and means for initiating operation of all of the motors in the same direction through the same predetermined range regardless of the individual settings of the selector switches.

10. In a contour systems for stage encore curtains or the like, in combination, a plurality of cable hoist reeling drums, reversible direct cur- 20 mm; motors individual to each of said drums, driving connections between each drum and its associated motor including self-locking worm gearing, control ystems individual to each of said motors to be subjected to supply from an alternating current source comprising means settable at will to preselect anyone of a plurality of preset but adjustable ranges of operation for its associated motorand means for supplying the armature of said associated motor with rectified current including means responsive to the setting of the first mentioned means to regulate the armature current in accordance with the range of operation selected for its associated motor, and control means common to the control systems of all of said motors for initiating operation of all of said motors in the same direction simultaneously. I

RAUL M. FISCHER.

REFERENCES CITED The following references are of record'in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,002,268 Lassen et al May 21, 1935 2,032,107 Boyle Feb. 25, 1936 

